1. Field of the Invention
This invention relates to devices for enabling sequential percutaneous dilation of a tissue opening to permit subsequent insertion of a large cannula. More particularly, the present invention pertains to a sequential dilator system that utilizes a series of telescoping dilators of gradually increasing size.
2. Prior Art
Numerous procedures exist for obtaining percutaneous access to the vascular system. For example, percutaneous vascular catheterization for small diameter cannulae has been accomplished by use of a thin wall entry needle in accordance with the Seldinger technique. Acta Radiologica, 38:368-376, 1953. This involves passing a guide wire through the lumen of the entry of the needle for proper positioning within the vessel. The needle is then withdrawn and a small catheter is inserted over the guide wire and twisted through the tissue opening with minimal trauma. The guide wire is then removed and the cannula is placed in operation.
Although similar placement of small diameter cannulae is routinely done thousands of times each day in hospitals, placement of larger cannulae has been limited. For example, cannulae needed for delivery of up to six liters of blood flow per minute requires a large percutaneous opening for cannulae of up to 28 French in size. In the past, a surgical cut-down procedure requiring the presence of a surgeon has been necesary.
More recently, techniques have been developed which enable gradual dilation of a small percutaneous opening to the required large size. Tapered dilators have been developed which are small at the tip and which increase in diameter to a desired dilation radius. Such tapered design, however, is not well suited for telescopic emplacement of the cannulae, whose diameter is generally uniform to provide better flow dynamics. Therefore, introduction of large cannulae by dilators with extreme tapered configuration has not been practical.
Other techniques have been developed in prototype stage which provide gradual dilation without cut-down. One such method utilizes a device manufactured by Adam Spence Corporation of Wall, New Jersey, as part of procedure for removing kidney stones. This device comprises a series of telescoping tubes, each tube having a uniform diameter slightly larger than the tube diameter which is inserted within its bore. These tubes may be slid in both directions in telescoping relationship and pose the problem of smaller tube ends sliding within the bore of a larger tube, thereby losing grasp of the tube end for withdrawal. In essence each smaller tube has substantially greater length than the larger tubes, and basically operates as a guide wire for the next tube mounted thereon. This pattern of decreasing the length of the tube with increasing diameter requires the physician to guess as to the desired positioning location of each telescoping section. Obviously, there is no guarantee that correct positioning will remain during patient use even if the correct position is initially applied. This unpredictable character not only increases risk to the patient, but also adds difficulty to the attending medical staff. The device is not well-suited for use within the circulatory system.
It would be desirable to have a more rapid and simplistic approach to patient cannulation which does not depend on the exercise of extreme care by medical staff for proper emplacement of the catheter. Such procedures are particularly needed for the growing number of frequent emergency extracorporeal cardio-pulmonary bypass operations. Furthermore, a true percutaneous method of cannulation would eliminate the need for surgical cut-down often practiced with respect to cannulation of the femoral vein and artery, thereby allowing a broader range of hospital based physicians to implement the procedure.